We hypothesize that the fish oils, EPA and DHA, can serve as effective chemopreventive agents against lung cancer and that this protective effect is mediated by selective alteration of arachidonate metabolism through cyclooxygenase enzymes to favor production of PGE3 rather than PGE2. The beneficial effect of PGE3 (i.e. inhibition of tumor cell proliferation vs stimulation produced by PGE2) is at present a poorly understood phenomenon. The research proposed in this application will help us determine the efficacy of fish oil against human lung cancer and obtain insight into the pharmacodynamic activity of EPA and DHA on normal and malignant lung epithelial cells. The specific aims of this proposed project are as follows: 1. To compare the time and concentration-dependent inhibitory effect of EPA and DHA alone or in combination on growth of human lung tumor cells, including cells expressing high and low levels of COX-2. 2. To determine changes in eicosanoid metabolism in human normal and cancer lung cells resulting from exposure of cells to EPA and DHA. The relative effect of these fish oils will also be examined against purified human recombinant COX-1 or COX-2 enzymes using our new and highly specific LC/MS/MS method that simultaneously and rapidly determines prostaglandins (e.g. PGE2 and PGE3) as well as selected lipoxygenase enzyme products (5-, 8-, 11-, 12-, and 15-HETE as well as specific leukotrienes such as LTB4 and LTB5). 3. To compare the relative effect of PGE2 and PGE3 at physiological and pharmacological concentrations on lung cell proliferation and mobility. 4. To study the relationship of PGE2 and PGE3 on cell proliferation and motility relative to activation of the cAMP-PKA signaling pathway through prostanoid receptors in human normal and cancer cells, and 5. To evaluate the relative efficacy of EPA, DHA and fish oil (containing both fatty acids) in prevention of tumor growth and its correlation to alteration of eicosanoid metabolism in a mouse model of human lung cancer.